At 04:19 PM 11/8/98 -0000, John V Jackson wrote:
>--Original Message-- From: Stanley Friesen <sarima@ix.netcom.com>Date: 08
>>It needn't be all that weird.
>>
>>A) Most Jurassic pterosaurs are found in only two or three lagerstaetten,
>>all lakes or lagoons.
>>
>>B) Pterosaurs can fly, basal maniraptorans most likely could not. Ergo,
>>pterosaurs are more likely to die where they can end up in a lake than are
>>the terrestrial mani's.
>
>Yes, but the issue is not "Where are the pterosaurs?" - I
>brought those up to show the J wasn't that bad compared to the
>K. I know some animals really don't preserve well - the *true*
>ancestors of Archae for example, but the real issue is "Where
>are those larger terrestrial/'cursorial' maniraptorans?"
>
Who says there *were* any? The basal maniraptorans seem to be small forms,
so it is quite likely that the entire pre-Cretaceous maniraptoran lineage
is composed of small animals. (In fact I suspect that most maniraptorans -
at ALL times - were arboreal as well, and that the known Cretaceous
maniraptorans are very atypical, even for that time, in being large and
secondarily terrestrial).
That is why the taphonomic factors matter. Small, non-flying (or
semi-flying) arboreal/terrestrial forms are FAR less likely to be preserved
in the fossil record than similarly sized flying forms - especially if
those flying forms were aerial insectivores that regularly flew over the
water to feed. Thus the near absence of maniraptorans in the Jurassic may
be a simple, and quite normal, artifact of known and prosaic taphonomic
biases.
[Note, even if the early maniraptorans were gliders, as George suggests,
they would not be feeding "on the wing", as most of the Solnhofen
pterosaurs probably were: swifts, swallows, and ducks are more likely to be
preserved than flying squirrels, or even parrots; the Solnhofen pterosaurs
were apparently the swift and falcon equivalents of the Jurassic].
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May the peace of God be with you. sarima@ix.netcom.com